The present invention relates to a chair having a backrest support biased or stressed against the back of a user with an energy storing device having a manually adjustable pre-set tension.
A chair of this type is described in European Patent Application 0 277 474 A1, in which the seat part is height-adjustably mounted on the seat support against the prestress of a spring element by means of a parallelogram guide bar arrangement. The backrest support is mounted on the seat support such that it can swivel, such that the backrest support is pivoted against the prestressing force of the spring element. However, it is not possible to manually influence or adjust the prestressing force of the spring element.
In German Patent Application 198 10 768 A1, another synchronizing mechanism is known, in which there is an energy storing device, not prestressed by the backrest support, in the form of a helical spring. In this known arrangement, the prestress of the helical spring may be changed through a mechanical gear, which is impinged on by a button rotatable by hand. This involves a synchronizing mechanism, in which the spring resistance of the helical spring may be adjusted through a hand adjustment. When lowering the backrest support, the seat plate is guided backwards via a diagonal slot directed backwards, as a result of which the spring is stretched. The relatively difficult guide between the seat and the backrest support is a disadvantage, and furthermore, it is a further disadvantage that the manual adjustment of the spring prestressing force through a spur gear system is costly and prone to breakdowns.